Liquid Metal Rotating Anode X-Ray Source For Semiconductor Metrology

ABSTRACT

Methods and systems for realizing a high brightness, liquid based x-ray source suitable for high throughput x-ray metrology are presented herein. A high brightness x-ray source is produced by bombarding a rotating liquid metal anode material with a stream of electrons to generate x-ray radiation. A rotating anode support structure supports the liquid metal anode material in a fixed position with respect to the support structure while rotating at the constant angular velocity. In another aspect, a translational actuator is coupled to the rotating assembly to translate the liquid metal anode in a direction parallel to the axis of rotation. In another aspect, an output window is coupled to the rotating anode support structure. Emitted x-rays are transmitted through the output window toward the specimen under measurement. In another further aspect, a containment window maintains the shape of the liquid metal anode material independent of rotational angular velocity.

CROSS REFERENCE TO RELATED APPLICATION

The present application for patent claims priority under 35 U.S.C. § 119from U.S. provisional patent application Ser. No. 62/573,958, entitled“X-Ray Source with Liquid Metal Rotating Anode (LiMeRa) forSemiconductor Metrology,” filed Oct. 18, 2017, the subject matter ofwhich is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The described embodiments relate to metrology systems and methods, andmore particularly to methods and systems for improved illumination.

BACKGROUND INFORMATION

The various features and multiple structural levels of semiconductordevices such as logic and memory devices are typically fabricated by asequence of processing steps applied to a specimen. For example,lithography among others is one semiconductor fabrication process thatinvolves generating a pattern on a semiconductor wafer. Additionalexamples of semiconductor fabrication processes include, but are notlimited to, chemical-mechanical polishing, etch, deposition, and ionimplantation. Multiple semiconductor devices may be fabricated on asingle semiconductor wafer and then separated into individualsemiconductor devices.

Metrology processes are used at various steps during a semiconductormanufacturing process to detect defects on wafers to promote higheryield. Optical metrology techniques offer the potential for highthroughput without the risk of sample destruction. A number of opticalmetrology based techniques including scatterometry and reflectometryimplementations and associated analysis algorithms are commonly used tocharacterize critical dimensions, film thicknesses, composition andother parameters of nanoscale structures.

As devices (e.g., logic and memory devices) move toward smallernanometer-scale dimensions, characterization becomes more difficult.Devices incorporating complex three-dimensional geometry and materialswith diverse physical properties contribute to characterizationdifficulty. For example, modern memory structures are often high-aspectratio, three-dimensional structures that make it difficult for opticalradiation to penetrate to the bottom layers. In addition, the increasingnumber of parameters required to characterize complex structures (e.g.,FinFETs), leads to increasing parameter correlation. As a result, theparameters characterizing the target often cannot be reliably decoupledwith available measurements. In another example, opaque, high-kmaterials are increasingly employed in modern semiconductor structures.Optical radiation is often unable to penetrate layers constructed ofthese materials. As a result, measurements with thin-film scatterometrytools such as ellipsometers or reflectometers are becoming increasinglychallenging.

In response, more complex optical tools have been developed. Forexample, tools with multiple angles of illumination, shorter and broaderranges of illumination wavelengths, and more complete informationacquisition from reflected signals (e.g., measuring multiple Muellermatrix elements in addition to the more conventional reflectivity orellipsometric signals) have been developed. However, these approacheshave not reliably overcome fundamental challenges associated withmeasurement of many advanced targets (e.g., complex 3D structures,structures smaller than 10 nm, structures employing opaque materials)and measurement applications (e.g., line edge roughness and line widthroughness measurements).

Atomic force microscopes (AFM) and scanning-tunneling microscopes (STM)are able to achieve atomic resolution, but they can only probe thesurface of the specimen. In addition, AFM and STM microscopes requirelong scanning times. Scanning electron microscopes (SEM) achieveintermediate resolution levels, but are unable to penetrate structuresto sufficient depth. Thus, high-aspect ratio holes are not characterizedwell. In addition, the required charging of the specimen has an adverseeffect on imaging performance.

To overcome penetration depth issues, traditional imaging techniquessuch as TEM, SEM etc., are employed with destructive sample preparationtechniques such as focused ion beam (FIB) machining, ion milling,blanket or selective etching, etc. For example, transmission electronmicroscopes (TEM) achieve high resolution levels and are able to probearbitrary depths, but TEM requires destructive sectioning of thespecimen. Several iterations of material removal and measurementgenerally provide the information required to measure the criticalmetrology parameters throughout a three dimensional structure. But,these techniques require sample destruction and lengthy process times.The complexity and time to complete these types of measurementsintroduces large inaccuracies due to drift of etching and metrologysteps. In addition, these techniques require numerous iterations whichintroduce registration errors.

Another response to recent metrology challenges has been the adoption ofx-ray metrology for measurements including film thickness, composition,strain, surface roughness, line edge roughness, and porosity.

Small-Angle X-Ray Scatterometry (SAXS) systems have shown promise toaddress challenging measurement applications. Various aspects of theapplication of SAXS technology to the measurement of critical dimensions(CD-SAXS) and overlay (OVL-SAXS) are described in 1) U.S. Pat. No.7,929,667 to Zhuang and Fielden, entitled “High-brightness X-raymetrology,” 2) U.S. Patent Publication No. 2014/0019097 by Bakeman,Shchegrov, Zhao, and Tan, entitled “Model Building And Analysis EngineFor Combined X-Ray And Optical Metrology,” 3) U.S. Patent PublicationNo. 2015/0117610 by Veldman, Bakeman, Shchegrov, and Mieher, entitled“Methods and Apparatus For Measuring Semiconductor Device Overlay UsingX-Ray Metrology,” 4) U.S. Patent Publication No. 2016/0202193 by Hench,Shchegrov, and Bakeman, entitled “Measurement System Optimization ForX-Ray Based Metrology,” 5) U.S. Patent Publication No. 2017/0167862 byDziura, Gellineau, and Shchegrov, entitled “X-ray Metrology For HighAspect Ratio Structures,” and 6) U.S. Patent Publication No.2018/0106735 by Gellineau, Dziura, Hench, Veldman, and Zalubovsky,entitled “Full Beam Metrology for X-Ray Scatterometry Systems.” Theaforementioned patent documents are assigned to KLA-Tencor Corporation,Milpitas, Calif. (USA).

Research on CD-SAXS metrology of semiconductor structures is alsodescribed in scientific literature. Most research groups have employedhigh-brightness X-ray synchrotron sources which are not suitable for usein a semiconductor fabrication facility due to their immense size, cost,etc. One example of such a system is described in the article entitled“Intercomparison between optical and x-ray scatterometry measurements ofFinFET structures” by Lemaillet, Germer, Kline et al., Proc. SPIE,v.8681, p. 86810Q (2013). More recently, a group at the NationalInstitute of Standards and Technology (NIST) has initiated researchemploying compact and bright X-ray sources similar those described inU.S. Pat. No. 7,929,667. This research is described in an articleentitled “X-ray scattering critical dimensional metrology using acompact x-ray source for next generation semiconductor devices,” J.Micro/Nanolith. MEMS MOEMS 16(1), 014001 (January-March 2017).

SAXS has also been applied to the characterization of materials andother non-semiconductor related applications. Exemplary systems havebeen commercialized by several companies, including Xenocs SAS(www.xenocs.com), Bruker Corporation (www.bruker.com), and RigakuCorporation (www.rigaku.com/en).

Many x-ray metrology techniques used in semiconductor manufacturing canbenefit from high brightness x-ray sources. For example, criticaldimension small angle x-ray scattering (CD-SAXS) measurements oftenrequire long integration times due to the low scattering of certainmaterials. A high brightness source can improve the throughput ofCD-SAXS measurements.

Development efforts in the area of extreme ultraviolet (EUV) lithographyare focused on light sources that emit narrowband radiation (e.g.,+/−0.1 nm) centered at 13 nanometers (i.e., 92.6 electron volts) at highpower levels (e.g., 210 watts of average power at the intermediate focusof the illuminator). Light sources for EUV lithography have beendeveloped using a laser droplet plasma architecture. For example, xenon,tin, and lithium droplet targets operating at pulse repetitionfrequencies of approximately 100 kHz are pumped by CO2 coherent sources.The realized light is high power (e.g., 210 watts of average power atthe intermediate focus of the illuminator is the goal for lithographytools at 13 nanometers). However, the resulting radiation is relativelylow energy (92.6 electron volts), which severely limits the utility ofthese illumination sources in metrology applications. An exemplarysystem is described in U.S. Pat. No. 7,518,134 to ASML Netherlands B.V.,the content of which is incorporated herein by reference in itsentirety.

In some examples, x-ray illumination light is generated by high energyelectron beam bombardment of a solid target material, such as rotatinganode target material. Rotating anode X-ray sources are commonlyemployed for medical imaging and analytical chemistry applications.Numerous versions of rotating anode X-ray sources are manufactured bycompanies such as Philips, General Electric, Siemens, and others, formedical imaging applications such as tomography, mammography,angiography, etc. Rigaku Corporation and Bruker Corporation manufacturecontinuously operated rotating anode sources for analytical chemistryapplications such as X-Ray diffraction (XRD), X-Ray Reflectometry (XRR),small angle X-Ray scatterometry (SAXS), wide angle X-Ray scatterometry(WARS), etc.

Rotating anode targets enable more effective heat removal from the anodematerial compared to stationary anode targets. Continuously moving thelocation of electron beam impingement on the anode surface results inconvective heat dissipation that decreases focal spot impact temperatureand improves X-ray tube power loading capability. A typical rotatinganode source rotates anode material at 5,000-10,000 revolutions perminute, or higher. The linear speed of the anode material at the focalspot location may be 100 meters/second, or higher.

Improvements directed toward increased anode heat dissipation andthermal conductivity have been proposed. For example, the FR-X modelX-ray sources manufactured by Rigaku Corporation (Japan) and theMicroMax model X-ray sources manufactured by Bruker AXS GmbH (Germany)employ water cooling to dissipate heat generated at the anode.

U.S. Pat. No. 9,715,989 describes a rotating anode structure with highthermal conductivity diamond layers. U.S. Pat. No. 8,243,884 describesthe use of diamond-metal composite materials to improve heatdissipation. U.S. Pat. No. 7,440,549 describes a rotating anode devicethat dissipates heat by a heat pipe effect. U.S. Patent Publication No.2015/0092924 describes a microstructural anode including a high atomicnumber material embedded in a high thermal conductivity matrix. U.S.Pat. No. 9,159,524 and U.S. Pat. No. 9,715,989 describe similardiamond-based heat management solutions in the context of stationaryanode sources. The contents of the aforementioned U.S. Patents and U.S.Patent Publications are incorporated herein by reference in theirentirety.

Despite improved power loading capabilities, rotating anode sourcessuffer from significant limitations. In practice, microcracks form atthe surface of the solid anode material located on the focal track(i.e., the locus of points repeatedly subjected to e-beam impingement)due to repeated thermal cycling. These microcracks introduce losses dueto increased absorption. In some examples, a 20-30% drop in X-ray fluxoccurs within the first 1,000 hours of source operation. In addition, atypical rotating anode requires re-polishing (i.e., restoration of thesurface of the anode material) approximately every 3,000 hours. Inaddition, in some examples, high rotation speeds limit X-ray spot sizeand spatial stability of the X-ray spot.

In some other examples, x-ray illumination light is generated by highenergy electron beam bombardment of a liquid target material to mitigatethe formation of surface microcracks associated with solid anodetargets.

In some of these examples, a liquid metal jet anode is employed. Anexemplary liquid metal jet x-ray illumination system is described inU.S. Pat. No. 7,929,667 to Zhuang and Fielden, the content of which isincorporated herein by reference in its entirety. Another exemplaryliquid metal jet x-ray illumination source is described in U.S. Pat. No.6,711,233, the content of which is incorporated herein by reference inits entirety. The liquid metal jet effectively refreshes the anodesurface continuously to eliminate the formation of surface microcracks.However, the liquid metal anode material does evaporate and form a metalvapor that may limit x-ray source lifetime. In some examples, the metalvapor condenses on the vacuum x-ray window causing additional x-rayabsorption. In some examples, the metal vapor diffuses into the cathoderegion and contaminates the cathode, reducing cathode lifetime andsystem output. In some examples, the metal vapor diffuses into theelectron beam acceleration region causing high-voltage breakdowns.

In some other examples, a liquid metal anode is flowed over a stationarystructure. U.S. Pat. No. 4,953,191 describes a liquid metal anodematerial flowing over a stationary metal surface, the content of whichis incorporated herein by reference in its entirety. U.S. Pat. No.8,629,606 describes a liquid metal anode material flowing on internalsurfaces of an X-ray source vacuum enclosure, the content of which isincorporated herein by reference in its entirety. U.S. PatentPublication No. 2014/0369476 and U.S. Pat. No. 8,565,381 describe aliquid metal anode material flowing through a channel or tube, thecontent of each is incorporated herein by reference in its entirety. Thefast moving liquid metal is enclosed in part by suitable windows toallow electron beam penetration and X-ray extraction.

Despite improved power loading capabilities, liquid anode sources sufferfrom significant limitations. In practice, flowing thin liquid metallayers over other surfaces is limited to relatively low velocity flow.As flow velocity increases, turbulence arises, which destabilizes theX-ray illumination source. As a result, anode power loading of an X-raysource employing liquid anode material flowing over another surface issignificantly limited. In addition, anode power loading for X-rayillumination sources based on flowing liquid metal inside channels andtubes is limited by the structural integrity of any windows employed tocontain the flow and allow electron beam penetration and X-rayextraction.

Similarly, stable operation of a liquid metal jet X-ray illuminationsource requires a laminar liquid metal jet flow. Therefore, any increasein jet speed to accommodate increased anode power loading is limited bythe laminar-turbulent transition of the jet itself and the feasibilityof an ultra-high-pressure jet return loop required to achieve anyincreased jet velocity.

Unfortunately, X-ray based metrology throughput is impaired by limitedpower loading on the anode. An increase in power loading of aconventional solid metal anode source causes ablation and destruction ofthe anode. For typical liquid metal sources, an increase in powerloading tends to destabilize the X-ray illumination source.

Future metrology applications present challenges for metrology due toincreasingly high resolution requirements, multi-parameter correlation,increasingly complex geometric structures, and increasing use of opaquematerials. The adoption of x-ray metrology for semiconductorapplications requires improved x-ray sources with the highest possiblebrightness.

SUMMARY

Methods and systems for realizing a high brightness, liquid based x-raysource suitable for high throughput x-ray metrology are presentedherein.

In one aspect, a high brightness x-ray source is produced by bombardinga rotating liquid metal anode material with a stream of electrons togenerate x-ray radiation. A rotating anode support structure supportsthe liquid metal anode material in a fixed position with respect to therotating anode support structure while the rotating anode supportstructure is rotating at the constant angular velocity. The resultingx-ray emission is collected and provided to a semiconductor specimen toperform x-ray based metrology on the specimen.

The liquid metal material surface does not degrade (e.g., crack) undercyclic thermal stress induced by periodic bombardment by the stream ofelectrons. The liquid metal material surface is effectivelyself-healing, which is a significant advantage over solid anodematerials. As a result, the rotating anode, liquid metal x-ray sourceimproves brightness and reliability, increases the time interval betweenservice, and decreases down time compared to traditional rotating solidanode x-ray sources.

In another aspect, x-ray optics are configured at specific collectionangles to capture x-ray emission in the desired energy band at peakintensity. In some embodiments, x-ray optics are designed to directlyfocus x-ray radiation to the measurement target. In some embodiments,x-ray collection optics are oriented in such a way as to optimize x-raybrightness by collecting x-ray radiation over a range of collectionangles.

In a further aspect, a translational actuator is coupled to the rotatingassembly that causes the rotating assembly to also translate in adirection parallel to the axis of rotation.

In another further aspect, an output window is coupled to the rotatinganode support structure, and x-rays emitted by the liquid metal anodematerial are transmitted through the output window toward the specimenunder measurement.

In another further aspect, a containment window is coupled to therotating anode support structure, and the incident stream of electronsare transmitted through the containment window before incidence withliquid metal anode material.

The foregoing is a summary and thus contains, by necessity,simplifications, generalizations and omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is not limiting in any way. Other aspects,inventive features, and advantages of the devices and/or processesdescribed herein will become apparent in the non-limiting detaileddescription set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrative of an x-ray metrology system 100 forperforming semiconductor metrology measurements including a liquid metalrotating anode (LiMeRa) x-ray illumination source in at least oneaspect.

FIG. 2A is a diagram illustrative of an instance of a rotating anodeassembly of a (LiMeRa) x-ray illumination source in one embodiment.

FIG. 2B is a diagram illustrative of another instance of the rotatinganode assembly of a (LiMeRa) x-ray illumination source in the embodimentillustrated in FIG. 2A.

FIG. 3 depicts a rotating anode assembly of a LiMeRa x-ray illuminationsource in another embodiment.

FIG. 4 depicts a rotating anode assembly of a LiMeRa x-ray illuminationsource in yet another embodiment.

FIG. 5 depicts a rotating anode assembly of a LiMeRa x-ray illuminationsource in yet another embodiment.

FIG. 6A is a diagram illustrative of an instance of a rotating anodeassembly of a (LiMeRa) x-ray illumination source in yet anotherembodiment.

FIG. 6B is a diagram illustrative of another instance of the rotatinganode assembly of a (LiMeRa) x-ray illumination source in the embodimentillustrated in FIG. 5A.

FIG. 7 depicts a rotating anode assembly of a LiMeRa x-ray illuminationsource in yet another embodiment.

FIG. 8 is a diagram illustrative of an x-ray detector 123 of x-raymetrology system 100 contained in a vacuum environment 172 separate fromspecimen 101.

FIG. 9 is a diagram illustrative of an x-ray metrology system 200 forperforming semiconductor metrology measurements including a LiMeRa x-rayillumination source.

FIG. 10 is a flowchart illustrative of an exemplary method 300 suitablefor generating x-ray emission from a LiMeRa x-ray illumination source.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings.

Systems employed to measure structural and material characteristics(e.g., material composition, dimensional characteristics of structuresand films, etc.) associated with different semiconductor fabricationprocesses based on x-ray illumination are presented. More specifically,methods and systems for realizing a high brightness, liquid based x-raysource suitable for high throughput x-ray metrology are presentedherein.

In one aspect, a high brightness x-ray source is produced by bombardinga rotating liquid metal anode material with a stream of electrons togenerate x-ray radiation. The resulting x-ray emission is collected andprovided to a semiconductor specimen to perform x-ray based metrology onthe specimen.

The liquid metal material surface does not degrade (e.g., crack) undercyclic thermal stress induced by periodic bombardment by the stream ofelectrons. The liquid metal material surface is effectivelyself-healing, which is a significant advantage over solid anodematerials. As a result, the rotating anode, liquid metal x-ray sourceimproves brightness and reliability, increases the time interval betweenservice, and decreases down time compared to traditional rotating solidanode x-ray sources.

Furthermore, by eliminating the problem of surface degradation, overallpower loading on the liquid metal anode material may be increased. Inaddition, the incident electron beam may be focused with greaterintensity to yield brighter x-ray emission useable for semiconductormetrology.

The high energy nature of x-ray radiation allows for the penetration ofx-rays into optically opaque thin films, buried structures, high-aspectratio structures and devices containing many thin film layers. Manyx-ray metrology techniques used in semiconductor manufacturing benefitfrom a high brightness, reliable x-ray source, e.g., critical dimensionsmall angle x-ray scattering (CD-SAXS).

Measurements often need long integration times due to the low scatteringefficiency of materials comprising many modern semiconductor structures.A high brightness high power liquid metal rotating anode x-ray sourceimproves the throughput of x-ray based measurements, e.g., CD-SAXS.

FIG. 1 illustrates an embodiment of an x-ray based metrology system 100including a liquid metal rotating anode (LiMeRa) x-ray illuminationsource in one embodiment. By way of non-limiting example, x-raymetrology system 100 operates in a transmission mode. As depicted inFIG. 1, the LiMeRa x-ray illumination source includes an electron beamsource 103 and a rotating anode assembly 110.

The rotating anode assembly 110 includes a rotational actuator 112 thatrotates a rotating anode support structure 111 about an axis ofrotation, A, at an angular velocity, ω. The rotating anode assembly 110also includes a liquid metal anode material 113 supported by rotatinganode support structure 111. The rotation induces a centrifugal force onliquid metal anode material 113 that conforms liquid metal anodematerial 113 to the shape of the rotating anode support structure 111,and distributes the liquid metal anode material 113 evenly along thecircumference of the rotating anode support structure 111. At constantangular velocity, a steady state distribution of liquid metal anodematerial 113 on the surface of rotating anode support structure 111, andthe liquid metal anode material 113 is not moving with respect to therotating anode support structure 111. In other words, the liquid metalanode material 113 and the rotating anode support structure 111 aremoving together with respect to the electron beam source 103, but notwith respect to one another.

In the embodiment depicted in FIG. 1, computing system 130 iscommunicatively coupled to rotary actuator 112. In one example, commandsignals 136 are communicated to rotary actuator 112 from computingsystem 130 indicating a desired angular velocity of the rotating anodesupport structure 111. In response, rotary actuator 112 adjusts theangular velocity of the rotating anode support structure 111 based onthe command signals 136.

In the embodiment depicted in FIG. 1, the LiMeRa x-ray illuminationsource provides high brightness x-ray illumination delivered to aspecimen 101 over an inspection area 102. X-ray metrology system 100 isconfigured such that x-rays which interact with the specimen 101 arecollected by a detector 123 while a specimen positioning system 140positions the specimen to produce angularly resolved interactions of thesample with the x-rays. In some embodiments, any other particlesproduced during the interaction such as photoelectrons, x-rays producedthrough fluorescence, or ions may also be detected.

In the embodiment depicted in FIG. 1, the LiMeRa x-ray illuminationsource includes an electron beam source 103 (e.g., electron gun)configured to generate electron emission from a cathode. In the depictedembodiment, electron beam source 103 generates a stable stream of freeelectrons 105. The stream of electrons 105 is shaped by electron optics104 and is incident on liquid metal anode material 113 supported byrotating anode support structure 111. In some embodiments, the electronbeam source 103 is configured to generate a continuous electron beam. Insome other embodiments, the electron beam source 103 is configured togenerate a pulsed electron beam.

In the embodiment depicted in FIG. 1, electron beam source 103 iscommunicatively coupled to computing system 130, and electron beamsource 103 is actively controlled based on command signals 135communicated from computing system 130 to electron beam source 103. Insome examples, command signals 135 include an indication of desiredelectron beam energy to be supplied by electron beam source 103. Inresponse, electron beam source 103 adjusts electron beam energy outputto the desired value. In some embodiments, the electron beam source 103accelerates the stream of focused electrons 105 with a voltagedifferential greater than 10 kV.

Electron optics 104 are configured to direct and/or focus the stream ofelectrons 105 toward the liquid metal anode material 113. Electronoptics 104 includes suitable electromagnets, permanent magnets, or anycombination of electromagnets and permanent magnets for focusing theelectron beam and directing the stream of electrons 105. In someembodiments, electron optics 104 may include solenoids, quadrupolelenses such as Halbach cylinders or electrostatic elements such asEinzel lenses to focus and direct the electron beam. In addition,electron optics 104 may be configured as an electron monochromator.Moreover, electron optics 104 may be employed to focus the beam tofurther reduce electron beam noise.

In addition, electron optics 104 may be configured for active control bycomputing system 130. In some embodiments (not shown), computing system130 is communicatively coupled to electron optics 104. In some examples,current or voltage supplied to electromagnetic elements may be activelycontrolled based on command signals communicated from computing system130 to electron optics 104. In another example, the position of amagnetic element (e.g., a permanent magnet) may be manipulated by apositioning system (not shown) based on command signals communicatedfrom computing system 130 to electron optics 104. In this manner, thefocusing and directing of the stream of electrons 105 is achieved underthe control of computing system 130 to achieve a stable stream ofelectrons 105 incident on liquid metal anode material 113.

As depicted in FIG. 1, x-ray optics 106 are configured to collect x-rayemission from the spot of incidence of the stream of electrons 105 andliquid metal anode material 113 and shape and direct incident x-ray beam108 to specimen 101.

In another aspect, x-ray optics 106 are configured at specificcollection angles to capture x-ray emission in the desired energy bandat peak intensity. In some embodiments, x-ray optics 106 are designed todirectly focus x-ray radiation to the measurement target. When a highenergy focused electron beam impinges upon a liquid metal anode target,the stimulated x-ray emission includes broadband Bremsstrahlungradiation and characteristic line emission (i.e., Kα, Kβ, Lα, Lβ, etc.).In some embodiments, x-ray collection optics are oriented in such a wayas to optimize x-ray brightness by collecting x-ray radiation over arange of collection angles.

In some examples, x-ray optics 106 monochromatize the x-ray beam that isincident on the specimen 101. In some examples, x-ray optics 106collimate or focus the x-ray beam 108 onto inspection area 102 ofspecimen 101. In some embodiments, x-ray optics 106 includes one or morex-ray collimating mirrors, x-ray apertures, x-ray monochromators, andx-ray beam stops, multilayer optics, refractive x-ray optics,diffractive optics such as zone plates, or any combination thereof.

In some embodiments, advanced x-ray optics such as polycapillary x-rayoptics, specular optics, or optics arranged in a Loxley-Tanner-Bowenconfiguration are employed to achieve high-brightness, small spot sizeillumination of a semiconductor specimen. For example, high intensityx-ray beams can be transported and focused to spot sizes of less than 40micrometers using specular x-ray optics such as grazing incidenceellipsoidal mirrors, polycapillary optics such as hollow capillary x-raywaveguides, multilayer optics, or crystalline optics such as aLoxley-Tanner-Bowen system.

In preferred embodiments, x-ray optics 106 are multilayer optics. Insome of these embodiments, multilayer optics are employed tomonochromatize the x-ray beam 108 to a spectral purity, δλ/λ, of lessthan 10−1. This level of spectral purity is suitable for metrologytechnologies such as x-ray reflectivity (XRR), x-ray diffraction (XRD),and x-ray fluorescence (XRF). In some other embodiments, crystalmonochromators are employed to monochromatize the x-ray beam 108 to aspectral purity, δλ/λ, of less than 10−6. This level of spectral purityis suitable for metrology technologies such as high resolution x-raydiffraction (HRXRD).

X-ray optics 106 may be configured for active control by computingsystem 130. In some embodiments, computing system 130 is communicativelycoupled to x-ray optics 106 (not shown). In one example, command signalscommunicated to x-ray optics 106 from computing system 130 indicate adesired position of an optical element. The position of the opticalelement may be adjusted by a positioning system (not shown) based on thecommand signal. In this manner, the focusing and directing of the x-raybeam 108 is achieved under the control of computing system 130 toachieve a stable illumination incident on specimen 101. In someexamples, computing system 130 is configured to control the positioningand spot size of the x-ray beam 108 incident on specimen 101. In someexamples, computing system 130 is configured to control illuminationproperties of the x-ray beam 108 (e.g., intensity, polarization,spectrum, etc.).

As depicted in FIG. 1, x-ray detector 123 collects x-ray radiation 122scattered from specimen 101 in response to the incident x-rayillumination and generates an output signal 124 indicative of propertiesof specimen 101 that are sensitive to the incident x-ray radiation.Scattered x-rays 122 are collected by x-ray detector 123 while specimenpositioning system 140 locates and orients specimen 101 to produceangularly resolved scattered x-rays.

As depicted in FIG. 1, the LiMeRa x-ray source is maintained in a vacuumenvironment maintained within vacuum chamber 120. X-ray emission passesthrough vacuum window 121 as the x-rays propagate from liquid metalanode material 113 toward x-ray optics 106.

FIG. 2A depicts rotating anode assembly 110 depicted in FIG. 1 in oneinstance. In the instance depicted in FIG. 2A, the angular velocity ofthe rotating anode assembly 110 is zero (i.e., at rest). In thisinstance, there are no centrifugal forces acting on liquid metal anodematerial 113. As a result, the gravitational forces acting on the liquidmetal anode material 113 dominate dynamic forces, and liquid metal anodematerial 113 conforms to the shape of rotating anode support structure111 in the direction perpendicular to the gravity vector, G. Rotatinganode support structure 111 is shaped such that liquid metal anodematerial 113 is constrained to remain in contact with rotating anodesupport structure 111 when angular velocity is zero. In other words,rotating anode support structure 111 is shaped such that liquid metalanode material 113 does not spill and is not lost when angular velocityis zero.

FIG. 2B depicts rotating anode assembly 110 depicted in FIG. 1 inanother instance. In the instance depicted in FIG. 2B, the angularvelocity of the rotating anode assembly 110 is a constant value, ω. Inthis instance, centrifugal forces act on liquid metal anode material113, in addition to the gravitational forces acting on the liquid metalanode material 113. As a result, the liquid metal anode material 113also conforms to the shape of rotating anode support structure 111 inthe direction parallel to the axis of rotation, A. Rotating anodesupport structure 111 is shaped such that liquid metal anode material113 is constrained to remain in contact with rotating anode supportstructure 111 when angular velocity is nonzero. In other words, rotatinganode support structure 111 is shaped such that liquid metal anodematerial 113 does not spill and is not lost when angular velocity isnonzero. In a further aspect, the rotating anode support structuresupports the liquid metal anode material in a fixed position withrespect to the rotating anode support structure while the rotating anodesupport structure is rotating at the constant angular velocity. In otherwords, the liquid metal anode material does not flow with respect to therotating anode support structure, while the rotating anode supportstructure is rotating at constant angular velocity.

In a further aspect, a translational actuator is coupled to the rotatingassembly that causes the rotating assembly to also translate in adirection parallel to the axis of rotation, A.

FIG. 3 depicts a rotating assembly 125 including rotating anode supportstructure 111, rotary actuator 112, liquid metal anode material 113, anda translational actuator 114. In the embodiment depicted in FIG. 3,translational actuator 114 is coupled to rotary actuator 112 andoscillates the rotating assembly with an amplitude, αH, in a directionparallel to axis of rotation, A. The rotational motion of the liquidmetal anode material 113 effectively changes the location of incidenceof the stream of electrons 105 with respect to the liquid metal anodematerial 113 circumferentially. The translational motion of the liquidmetal anode material 113 effectively changes the location of incidenceof the stream of electrons 105 with respect to the liquid metal anodematerial 113 in a direction parallel to the axis of rotation. Thiseffectively spreads the heat load imposed on the liquid metal anodematerial 113 by the stream of electrons 105 over a larger area.

In another further aspect, an output window is coupled to the rotatinganode support structure, and x-rays emitted by the liquid metal anodematerial are transmitted through the output window toward the specimenunder measurement.

FIG. 4 depicts a rotating assembly 126 including rotating anode supportstructure 111, rotary actuator 112, liquid metal anode material 113, andan output window 115. In the embodiment depicted in FIG. 4, an outputwindow 115 that is substantially transparent to x-ray radiation iscoupled to rotating anode support structure 111. X-rays 117 emitted fromliquid metal anode material 113 are transmitted through output window115. A metrology system, such as metrology system 100, includes x-rayoptical elements that collect and direct the transmitted x-ray radiation117 toward specimen 101 under measurement. In this manner, x-rayradiation is also collected in a tranmissive mode, rather than, or inaddition to x-ray radiation collected directly from the exposed surfaceof liquid metal anode material 113 (e.g., x-ray radiation 118).

In another further aspect, a containment window is coupled to therotating anode support structure, and the incident stream of electrons105 are transmitted through the containment window before incidence withliquid metal anode material 113.

FIG. 5 depicts a rotating assembly 127 including rotating anode supportstructure 111, rotary actuator 112, liquid metal anode material 113,output window 115, and containment window 116. In the embodimentdepicted in FIG. 5, a containment window 116 that is substantiallytransparent to the stream of electrons 105 is coupled to rotating anodesupport structure 111, and effectively constrains the liquid metal anodematerial 113 to a fixed shape with respect to the rotating anode supportstructure regardless of angular velocity. As depicted in FIG. 4B, liquidmetal anode material 113 is effectively trapped between containmentwindow 116 and output window 115. In this manner, liquid metal anodematerial 113 does not change shape regardless of angular velocity. Inembodiments that do not employ an output window, liquid metal anodematerial 113 is effectively trapped between containment window 116 androtating anode support structure 111. In the embodiment depicted in FIG.5, x-rays 117 emitted from liquid metal anode material 113 aretransmitted through output window 115, and x-ray radiation 118 is alsocollected directly from the exposed surface of liquid metal anodematerial 113. However, in general, x-ray radiation may be collecteddirectly from the exposed surface of liquid metal anode material 113, astransmitted through output window 115, or both.

FIGS. 1-4 depict embodiments of the rotating anode support structurethat support the liquid metal anode material such that the liquid metalanode material assumes a different shape when the rotating anode supportstructure is rotated at different, constant angular velocities. Morespecifically, the cross-sectional views of the liquid metal anodematerial 113 illustrated in FIGS. 1-4 show a cross-section of liquidmetal anode material which revolves around the axis of rotation, A, andthe exact cross-sectional shape depends on the angular velocity of therotation of the rotating anode support structure. In contrast, FIG. 5depicts an embodiment of the rotating anode support structure thatsupports the liquid metal anode material such that the liquid metalanode material assumes approximately the same shape independent of theangular velocity of the rotating anode support structure.

In general, many different shapes may be contemplated. FIGS. 6A-6Bdepict an embodiment 150 of a rotating assembly 150 including a rotatinganode support structure 151, a rotary actuator 152, and a liquid metalanode material 153. In the embodiment 150, the rotating supportstructure 151 supports the liquid metal anode material such that theliquid metal anode material assumes a toroidal shape while the rotatinganode support structure is rotated at constant angular velocity. Morespecifically, the cross-sectional views of the liquid metal anodematerial 153 illustrated in FIGS. 6A-6B show the liquid metal anodematerial conforming to a semicircular shape of the rotating anodesupport structure 151.

FIG. 6A depicts rotating anode assembly 150 in one instance. In theinstance depicted in FIG. 6A, the angular velocity of the rotating anodeassembly 150 is zero (i.e., at rest). In this instance, there are nocentrifugal forces acting on liquid metal anode material 153. As aresult, the gravitational forces acting on the liquid metal anodematerial 153 dominate dynamic forces, and liquid metal anode material153 conforms to the shape of rotating anode support structure 151 in thedirection perpendicular to the gravity vector, G. Rotating anode supportstructure 151 is shaped such that liquid metal anode material 153 isconstrained to remain in contact with rotating anode support structure151 when angular velocity is zero. In other words, rotating anodesupport structure 151 is shaped such that liquid metal anode material153 does not spill and is not lost when angular velocity is zero.

FIG. 6B depicts rotating anode assembly 150 in another instance. In theinstance depicted in FIG. 6B, the angular velocity of the rotating anodeassembly 150 is a constant value, ω. In this instance, centrifugalforces act on liquid metal anode material 153 in addition to thegravitational forces acting on the liquid metal anode material 153. As aresult, the liquid metal anode material 153 also conforms to the shapeof rotating anode support structure 151 in the direction parallel to theaxis of rotation, A. Rotating anode support structure 151 is shaped suchthat liquid metal anode material 153 is constrained to remain in contactwith rotating anode support structure 151 when angular velocity isnonzero. In other words, rotating anode support structure 111 is shapedsuch that liquid metal anode material 153 does not spill and is not lostwhen angular velocity is nonzero.

FIG. 7 depicts a rotating assembly 160 including rotating anode supportstructure 161, rotary actuator 162, liquid metal anode material 163, andcontainment window 164. In the embodiment depicted in FIG. 7, acontainment window 164 that is substantially transparent to the streamof electrons 105 is coupled to rotating anode support structure 161, andeffectively constrains the liquid metal anode material 163 to a fixedshape with respect to the rotating anode support structure regardless ofangular velocity. As depicted in FIG. 7, liquid metal anode material 163is effectively trapped between containment window 164 and rotating anodesupport structure 161. In this manner, liquid metal anode material 163does not change shape regardless of angular velocity. Liquid metal anodematerial 163 is effectively trapped between containment window 164 androtating anode support structure 161. In the embodiment depicted in FIG.7, x-rays 165 emitted from liquid metal anode material 163 aretransmitted through containment window 164.

In general, a rotating anode support structure, a containment window,and an output window may be fabricated from metal, graphite, diamond, orany combination of thereof.

In general, x-ray energy and generation efficiency scale with theelemental atomic number, Z, of the anode material. With some exceptions,the higher the atomic number, the higher the x-ray energy (i.e., shorterwavelength) and yield efficiency. Unfortunately, many materials having arelatively high atomic number also have high melting temperatures.

Liquid metal materials suitable for implementation as a liquid metalanode material in a LiMeRa x-ray illumination source as described hereininclude Gallium, Indium, Tin, Thallium, Cadmium, Bismuth, Lead,Antimony, Silver, Gold, and any combination thereof. In addition, liquidmetal anode alloys that include any of Gallium, Indium, Tin, Thallium,Cadmium, Bismuth, Lead, Antimony, Silver, and Gold may also becontemplated within the scope of this patent document. An example alloyis Wood's metal, which is a eutectic, fusible alloy with a melting pointof approximately 70° C. (158° F.). It is a eutectic alloy including 50%bismuth, 26.7% lead, 13.3% tin, and 10% cadmium by weight.

In a preferred example, the liquid metal anode material is Indium(Z=49), or an alloy including Indium. Conventional metals or refractorymaterials may be employed to stably support melted Indium. Furthermore,conventional heating devices may be employed to maintain liquid Indiumat a temperature above its melting point of 156° C. Similarly,conventional metals or refractory materials may be employed to stablysupport melted Tin (Z=50), and conventional heating devices may beemployed to maintain liquid Tin at a temperature above its melting pointof 232° C.

The coincidence of the liquid metal anode 113 and the stream ofelectrons 105 produces x-ray emission 108 incident on inspection area102 of specimen 101. A LiMeRa x-ray illumination source collects K-shellemission, L-shell emission, or a combination thereof, from the liquidmetal anode material. In some embodiments, it is preferred to have ax-ray source photon energy in a range from 10 keV to 25 keV to penetratethrough a silicon wafer with suitable transmission efficiency forTransmission Small Angle X-ray Scattering (T-SAXS) based semiconductormetrology applications such as critical dimension and overlay metrologyon patterned silicon wafers.

In some embodiments, the distance between specimen 101 and liquid metalanode material 113 is lengthy (e.g., greater than one meter). In theseembodiments, air present in the beam path introduces undesirable beamscattering. Hence, in some embodiments it is preferred to propagatex-ray beam 108 through an evacuated flight tube from the LiMeRaillumination source to specimen 101.

In some embodiments, the x-ray detector 123 is maintained in the sameatmospheric environment as specimen 101 (e.g., gas purge environment).However, in some embodiments, the distance between specimen 101 andx-ray detector 123 is lengthy (e.g., greater than one meter). In theseembodiments, air present in the beam path introduces undesirable beamscattering, especially when the LiMeRa illumination source is configuredto generate hard x-rays (e.g., photon energy greater than 5 keV). Hencein some embodiments, the x-ray detector 123 is maintained in alocalized, vacuum environment separated from the specimen (e.g.,specimen 101) by a vacuum window. FIG. 8 is a diagram illustrative of avacuum chamber 170 containing x-ray detector 123. In a preferredembodiment, vacuum chamber 170 includes a substantial portion of thepath between specimen 101 and x-ray detector 123. An opening of vacuumchamber 170 is covered by vacuum window 171. Vacuum window 171 may beconstructed of any suitable material that is substantially transparentto x-ray radiation (e.g., Kapton, Beryllium, etc.). Scattered x-rayradiation 122 passes through vacuum window 171, enters vacuum chamber170 and is incident on x-ray detector 123. A suitable vacuum environment172 is maintained within vacuum chamber 170 to minimize disturbances toscattered x-ray radiation 122.

In some embodiments, it is desirable to maintain the x-ray illuminationbeam 108, specimen 101, the collection beam 122, and detector 123 in anevacuated environment to minimize absorption of x-rays. This isespecially desirable if the LiMeRa illumination source is configured togenerate soft x-rays (e.g., photon energy less than 5 keV).

FIG. 9 illustrates an x-ray metrology system 200 for performingsemiconductor metrology measurements. By way of non-limiting example,x-ray metrology system 200 operates in a grazing incidence mode. Morespecifically, x-ray metrology system 200 is configured as a grazingincidence small-angle x-ray scattering (GISAXS) measurement system.Typical angles of incidence and collection are approximately one degreeas measured from the surface of the specimen, or approximately eightynine degrees from an axis normal to the surface of the specimen. X-raymetrology system 200 includes a LiMeRa x-ray illumination source asdescribed with reference to FIG. 1. As illustrated in FIG. 9, x-raymetrology system 200 includes similar, like numbered elements describedwith reference to

FIG. 1. X-ray metrology system 200 is configured such that x-rays whichare scattered from the specimen are collected by a detector while asample handler (not shown) positions the specimen. In addition any otherparticles produced during the interaction such as photoelectrons, x-raysproduced through fluorescence, or ions can be detected. Metrologysystems configured to perform GISAXS measurements require a highbrightness x-ray source to maintain sufficient brightness over therelatively large sample area illuminated at small angles. For thisreason, an LiMeRa x-ray illumination source is particularly well suitedfor GISAXS measurements.

By way of non-limiting example, the x-ray metrology system 100illustrated in FIG. 1 is configured as a transmission small angle x-rayscatterometer (TSAXS) and the x-ray metrology system 200 illustrated inFIG. 9 is configured as a grazing incidence small angle x-rayscatterometer (GISAXS). However, in general, an x-ray metrology systememploying a LiMeRa x-ray illumination source as described herein mayemploy any one or more of the following metrology techniques:transmission small angle x-ray scattering (TSAXS), grazing incidencesmall angle x-ray scattering (GISAXS), wide angle x-ray scattering(WAXS), x-ray reflectometry (XRR), grazing incidence x-ray reflectometry(GXR), x-ray diffraction (XRD), grazing incidence x-ray diffraction(GIXRD), high resolution x-ray diffraction (HRXRD), x-ray photoelectronspectroscopy (XPS), x-ray fluorescence (XRF), total reflection x-rayfluorescence (TXRF), grazing incidence x-ray fluorescence (GIXRF), x-raytomography, x-ray ellipsometry, and hard x-ray photoemissionspectrometry (HXPS).

X-ray metrology tool 100 also includes computing system 130 employed toacquire signals 124 generated by x-ray detector 123 and determineproperties of the specimen based at least in part on the acquiredsignals. As illustrated in FIG. 1, computing system 130 iscommunicatively coupled to x-ray detector 123. In one example, x-raydetector 123 is an x-ray spectrometer and measurement data 124 includesan indication of the measured spectral response of the specimen based onone or more sampling processes implemented by the x-ray spectrometer.Computing system 130 is configured to build models of the specimen,create x-ray simulations based upon the models, and analyze thesimulations and signals 124 received from x-ray detector 123 todetermine one or more characteristics of the sample (e.g., a value of aparameter of interest 180 of a structure under measurement).

In a further embodiment, computing system 130 is configured to accessmodel parameters in real-time, employing Real Time Critical Dimensioning(RTCD), or it may access libraries of pre-computed models fordetermining a value of at least one specimen parameter value associatedwith the specimen 101. In general, some form of CD-engine may be used toevaluate the difference between assigned CD parameters of a specimen andCD parameters associated with the measured specimen. Exemplary methodsand systems for computing specimen parameter values are described inU.S. Pat. No. 7,826,071, issued on Nov. 2, 2010, to KLA-Tencor Corp.,the entirety of which is incorporated herein by reference.

In one example, measurement data 124 includes an indication of themeasured x-ray response of the specimen. Based on the distribution ofthe measured x-ray response on the surface of detector 123, the locationand area of incidence of x-ray beam 108 on specimen 101 is determined bycomputing system 130. In one example, pattern recognition techniques areapplied by computing system 130 to determine the location and area ofincidence of x-ray beam 108 on specimen 101 based on measurement data124. In response computing system 130 generates command signals to anyof electron optics 104 and x-ray optics 109 to redirect and reshapeincident x-ray illumination beam 108.

In another aspect, x-ray measurements of a particular inspection areaare performed at a number of different out of plane orientations. Thisincreases the precision and accuracy of measured parameters and reducescorrelations among parameters by extending the number and diversity ofdata sets available for analysis to include a variety of large-angle,out of plane orientations. Measuring specimen parameters with a deeper,more diverse data set also reduces correlations among parameters andimproves measurement accuracy.

As illustrated in FIG. 1, x-ray metrology tool 100 includes a specimenpositioning system 140 configured to both align specimen 101 and orientspecimen 101 over a large range of out of plane angular orientationswith respect the LiMeRa x-ray illumination source. In other words,specimen positioning system 140 is configured to rotate specimen 101over a large angular range about one or more axes of rotation alignedin-plane with the surface of specimen 101. In some embodiments, specimenpositioning system 140 is configured to rotate specimen 101 within arange of at least 90 degrees about one or more axes of rotation alignedin-plane with the surface of specimen 101. In some embodiments, specimenpositioning system is configured to rotate specimen 101 within a rangeof at least 60 degrees about one or more axes of rotation alignedin-plane with the surface of specimen 101. In some other embodiments,specimen positioning system is configured to rotate specimen 101 withina range of at least one degree about one or more axes of rotationaligned in-plane with the surface of specimen 101. In this manner, angleresolved measurements of specimen 101 are collected by x-ray metrologysystem 100 over any number of locations on the surface of specimen 101.In one example, computing system 130 communicates command signals tomotion controller 145 of specimen positioning system 140 that indicatethe desired position of specimen 101. In response, motion controller 145generates command signals to the various actuators of specimenpositioning system 140 to achieve the desired positioning of specimen101. By way of non-limiting example, a specimen positioning system mayinclude any combination of a hexapod, linear, and angular stages.

By way of non-limiting example, as illustrated in FIG. 1, specimenpositioning system 140 includes an edge grip chuck 141 to fixedly attachspecimen 101 to specimen positioning system 140. A rotational actuator142 is configured to rotate edge grip chuck 141 and the attachedspecimen 101 with respect to a perimeter frame 143. In the depictedembodiment, rotational actuator 142 is configured to rotate specimen 101about the x-axis of the coordinate system 146 illustrated in FIG. 1. Asdepicted in FIG. 1, a rotation of specimen 101 about the z-axis is an inplane rotation of specimen 101. Rotations about the x-axis and they-axis (not shown) are out of plane rotations of specimen 101 thateffectively tilt the surface of the specimen with respect to themetrology elements of metrology system 100. Although it is notillustrated, a second rotational actuator is configured to rotatespecimen 101 about the y-axis. A linear actuator 144 is configured totranslate perimeter frame 143 in the x-direction. Another linearactuator (not shown) is configured to translate perimeter frame 143 inthe y-direction. In this manner, every location on the surface ofspecimen 101 is available for measurement over a range of out of planeangular positions. For example, in one embodiment, a location ofspecimen 101 is measured over several angular increments within a rangeof −45 degrees to +45 degrees with respect to the normal orientation ofspecimen 101.

The large, out of plane, angular positioning capability of specimenpositioning system 140 expands measurement sensitivity and reducescorrelations between parameters. For example, in a normal orientation,SAXS is able to resolve the critical dimension of a feature, but islargely insensitive to sidewall angle and height of a feature. However,collecting measurement data over a broad range of out of plane angularpositions enables the collection of measurement data associated with anumber of diffraction orders. This enables the sidewall angle and heightof a feature to be resolved. In addition, other features such asrounding or any other shapes associated with advanced structures can beresolved.

A x-ray metrology tool employing a high brightness liquid metal dropletx-ray source as described herein enables increased measurementsensitivity and throughput due to the high brightness and shortwavelength radiation (e.g., photon energy greater than 500 eV) generatedby the source. By way of non-limiting example, the x-ray metrology toolis capable of measuring geometric parameters (e.g., pitch, criticaldimension (CD), side wall angle (SWA), line width roughness (LWR), andline edge roughness (LER)) of structures smaller than 10 nanometers. Inaddition, the high energy nature of x-ray radiation penetrates opticallyopaque thin films, buried structures, high aspect ratio structures, anddevices including many thin film layers.

A x-ray metrology system employing a high brightness LiMeRa x-rayillumination source as described herein may be used to determinecharacteristics of semiconductor structures. Exemplary structuresinclude, but are not limited to, FinFETs, low-dimensional structuressuch as nanowires or graphene, sub 10 nm structures, thin films,lithographic structures, through silicon vias (TSVs), memory structuressuch as DRAM, DRAM 4F2, FLASH and high aspect ratio memory structures.Exemplary structural characteristics include, but are not limited to,geometric parameters such as line edge roughness, line width roughness,pore size, pore density, side wall angle, profile, film thickness,critical dimension, pitch, and material parameters such as electrondensity, crystalline grain structure, morphology, orientation, stress,and strain.

It should be recognized that the various steps described throughout thepresent disclosure may be carried out by a single computer system 130or, alternatively, a multiple computer system 130. Moreover, differentsubsystems of the system 100, such as the specimen positioning system140, may include a computer system suitable for carrying out at least aportion of the steps described herein. Therefore, the aforementioneddescription should not be interpreted as a limitation on the presentinvention but merely an illustration. Further, the one or more computingsystems 130 may be configured to perform any other step(s) of any of themethod embodiments described herein.

In addition, the computer system 130 may be communicatively coupled tothe x-ray detector 123, electron optics 104, x-ray optics 106, electronbeam source 103, rotary actuator 112, translational actuator 114, andspecimen positioning system 140 in any manner known in the art. Forexample, the one or more computing systems 130 may be coupled tocomputing systems associated with x-ray detector 123, electron optics104, x-ray optics 106, electron beam source 103, rotary actuator 112,translational actuator 114, and specimen positioning system 140,respectively. In another example, any of x-ray detector 123, electronoptics 104, x-ray optics 106, electron beam source 103, rotary actuator112, translational actuator 114, and specimen positioning system 140 maybe controlled directly by a single computer system coupled to computersystem 130.

The computer system 130 of the x-ray metrology system 100 may beconfigured to receive and/or acquire data or information from thesubsystems of the system (e.g., x-ray detector 123, electron optics 104,x-ray optics 106, electron beam source 103, rotary actuator 112,translational actuator 114, and specimen positioning system 140, and thelike) by a transmission medium that may include wireline and/or wirelessportions. In this manner, the transmission medium may serve as a datalink between the computer system 130 and other subsystems of the system100.

Computer system 130 of the metrology systems 100 and 200 may beconfigured to receive and/or acquire data or information (e.g.,measurement results, modeling inputs, modeling results, etc.) from othersystems by a transmission medium that may include wireline and/orwireless portions. In this manner, the transmission medium may serve asa data link between the computer system 130 and other systems (e.g.,memory on-board metrology system 100, external memory, or externalsystems). For example, the computing system 130 may be configured toreceive measurement data (e.g., output signals 124) from a storagemedium (i.e., memory 132) via a data link. For instance, spectralresults obtained using a spectrometer of x-ray detector 123 may bestored in a permanent or semi-permanent memory device (e.g., memory132). In this regard, the spectral results may be imported from on-boardmemory or from an external memory system. Moreover, the computer system130 may send data to other systems via a transmission medium. Forinstance, specimen parameter values 180 determined by computer system130 may be stored in a permanent or semi-permanent memory device. Inthis regard, measurement results may be exported to another system.

Computing system 130 may include, but is not limited to, a personalcomputer system, mainframe computer system, workstation, image computer,parallel processor, or any other device known in the art. In general,the term “computing system” may be broadly defined to encompass anydevice having one or more processors, which execute instructions from amemory medium.

Program instructions 134 implementing methods such as those describedherein may be transmitted over a transmission medium such as a wire,cable, or wireless transmission link. For example, as illustrated inFIG. 1, program instructions stored in memory 132 are transmitted toprocessor 131 over bus 133. Program instructions 134 are stored in acomputer readable medium (e.g., memory 132). Exemplary computer-readablemedia include read-only memory, a random access memory, a magnetic oroptical disk, or a magnetic tape.

In some embodiments, x-ray metrology as described herein is implementedas part of a fabrication process tool. Examples of fabrication processtools include, but are not limited to, lithographic exposure tools, filmdeposition tools, implant tools, and etch tools. In this manner, theresults of x-ray measurements are used to control a fabrication process.In one example, x-ray measurement data collected from one or moretargets is sent to a fabrication process tool. The x-ray data isanalyzed and the results used to adjust the operation of the fabricationprocess tool.

FIG. 10 illustrates a method 300 suitable for implementation by thex-ray metrology systems 100 and 200 of the present invention. In oneaspect, it is recognized that any data processing elements of method 300may be carried out via a pre-programmed algorithm executed by one ormore processors of computing system 130. While the following descriptionis presented in the context of x-ray metrology systems 100 and 200, itis recognized herein that the particular structural aspects of x-raymetrology system 100 do not represent limitations and should beinterpreted as illustrative only.

In block 301, a stream of electrons is emitted toward a liquid metalanode material from a cathode of an electron beam source. Theinteraction of the stream of electrons with the liquid metal anodematerial causes an x-ray emission.

In block 302, rotating anode support structure rotates about an axis ofrotation at a constant angular velocity. The rotating anode supportstructure supports the liquid metal anode material in a fixed positionwith respect to the rotating anode support structure while the rotatinganode support structure is rotating at the constant angular velocity.

In block 303, an amount of the x-ray emission is collected from theliquid metal anode material.

As described herein, the term “critical dimension” includes any criticaldimension of a structure (e.g., bottom critical dimension, middlecritical dimension, top critical dimension, sidewall angle, gratingheight, etc.), a critical dimension between any two or more structures(e.g., distance between two structures), and a displacement between twoor more structures (e.g., overlay displacement between overlayinggrating structures, etc.). Structures may include three dimensionalstructures, patterned structures, overlay structures, etc.

As described herein, the term “critical dimension application” or“critical dimension measurement application” includes any criticaldimension measurement.

As described herein, the term “metrology system” includes any systememployed at least in part to characterize a specimen in any aspect,including critical dimension applications and overlay metrologyapplications. However, such terms of art do not limit the scope of theterm “metrology system” as described herein. In addition, the metrologysystem 100 may be configured for measurement of patterned wafers and/orunpatterned wafers. The metrology system may be configured as a LEDinspection tool, edge inspection tool, backside inspection tool,macro-inspection tool, or multi-mode inspection tool (involving datafrom one or more platforms simultaneously), and any other metrology orinspection tool that benefits from a liquid droplet x-ray source.

Various embodiments are described herein for a semiconductor processingsystem (e.g., an inspection system or a lithography system) that may beused for processing a specimen. The term “specimen” is used herein torefer to a wafer, a reticle, or any other sample that may be processed(e.g., printed or inspected for defects) by means known in the art.

As used herein, the term “wafer” generally refers to substrates formedof a semiconductor or non-semiconductor material. Examples include, butare not limited to, monocrystalline silicon, gallium arsenide, andindium phosphide. Such substrates may be commonly found and/or processedin semiconductor fabrication facilities. In some cases, a wafer mayinclude only the substrate (i.e., bare wafer). Alternatively, a wafermay include one or more layers of different materials formed upon asubstrate. One or more layers formed on a wafer may be “patterned” or“unpatterned.” For example, a wafer may include a plurality of dieshaving repeatable pattern features.

A “reticle” may be a reticle at any stage of a reticle fabricationprocess, or a completed reticle that may or may not be released for usein a semiconductor fabrication facility. A reticle, or a “mask,” isgenerally defined as a substantially transparent substrate havingsubstantially opaque regions formed thereon and configured in a pattern.The substrate may include, for example, a glass material such asamorphous SiO2. A reticle may be disposed above a resist-covered waferduring an exposure step of a lithography process such that the patternon the reticle may be transferred to the resist.

One or more layers formed on a wafer may be patterned or unpatterned.For example, a wafer may include a plurality of dies, each havingrepeatable pattern features. Formation and processing of such layers ofmaterial may ultimately result in completed devices. Many differenttypes of devices may be formed on a wafer, and the term wafer as usedherein is intended to encompass a wafer on which any type of deviceknown in the art is being fabricated.

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A liquid metal rotating anode x-ray illuminationsource, comprising: an electron beam source configured to emit a streamof electrons toward a liquid metal anode material from a cathode of theelectron beam source, the interaction of the stream of electrons withthe liquid metal anode material causing an x-ray emission; and arotating anode assembly, comprising: a rotating anode support structureconfigured to rotate about an axis of rotation at a constant angularvelocity, wherein the rotating anode support structure supports theliquid metal anode material in a fixed position with respect to therotating anode support structure while the rotating anode supportstructure is rotated at the constant angular velocity; and a rotationalactuator coupled to the rotating anode support structure, wherein therotational actuator rotates the rotating anode support structure at theconstant angular velocity.
 2. The liquid metal rotating anode x-rayillumination source of claim 1, further comprising: at least one x-rayoptical element configured to collect an amount of the x-ray emissionfrom the liquid metal anode material.
 3. The liquid metal rotating anodex-ray illumination source of claim 2, wherein the collected amount ofx-ray emission is transmitted through a portion of the rotating anodeassembly from the liquid metal anode material to the at least one x-rayoptical element.
 4. The liquid metal rotating anode x-ray illuminationsource of claim 3, the rotating anode assembly further comprising: anoutput window coupled to the rotating anode support structure, whereinthe output window is transparent to the x-ray emission, and wherein thecollected amount of x-ray emission is transmitted through the outputwindow from the liquid metal anode material to the at least one x-rayoptical element.
 5. The liquid metal rotating anode x-ray illuminationsource of claim 1, the rotating anode assembly further comprising: acontainment window coupled to the rotating anode support structure,wherein the containment window constrains the liquid metal anodematerial to a fixed position with respect to the rotating anode supportstructure while the rotating anode support structure is rotated at theconstant angular velocity, wherein the containment window is transparentto the stream of electrons, and wherein the stream of electrons istransmitted through the containment window from the electron beam sourceto the liquid metal anode material.
 6. The liquid metal rotating anodex-ray illumination source of claim 1, the rotating anode assemblyfurther comprising: a translational actuator coupled to the rotatinganode support structure, wherein the translational actuator translatesthe rotating anode support structure in a direction parallel to the axisof rotation.
 7. The liquid metal rotating anode x-ray illuminationsource of claim 1, wherein the rotating anode support structure supportsthe liquid metal anode material such that the liquid metal anodematerial assumes a shape that depends on an angular velocity of rotationof the rotating anode support structure
 8. The liquid metal rotatinganode x-ray illumination source of claim 1, wherein the rotating anodesupport structure supports the liquid metal anode material such that across-section of the liquid metal anode material at any location along afocal track of the liquid metal rotating anode x-ray illumination sourceassumes a constant shape independent of an angular velocity of rotationof the rotating anode support structure.
 9. An x-ray based metrologysystem comprising: a liquid metal rotating anode x-ray illuminationsource configured to illuminate an inspection area of a specimen with anincident x-ray beam, wherein the liquid metal rotating anode x-rayillumination source includes, an electron beam source configured to emita stream of electrons toward a liquid metal anode material from acathode of the electron beam source, the interaction of the stream ofelectrons with the liquid metal anode material causing an x-rayemission; a rotating anode assembly, comprising: a rotating anodesupport structure configured to rotate about an axis of rotation at aconstant angular velocity, the rotating anode support structure supportsthe liquid metal anode material in a fixed position with respect to therotating anode support structure while the rotating anode supportstructure is rotated at the constant angular velocity; and a rotationalactuator coupled to the rotating anode support structure, wherein therotational actuator rotates the rotating anode support structure at theconstant angular velocity; at least one x-ray optical element configuredto collect an amount of the x-ray emission from the liquid metal anodematerial; and an x-ray detector configured to receive radiation from thespecimen in response to the incident x-ray beam and generate signalsindicative of a first property of the specimen.
 10. The x-ray basedmetrology system of claim 9, wherein the x-ray based metrology system isa small angle x-ray scatterometer configured to perform measurements ina transmissive or a reflective mode.
 11. The x-ray based metrologysystem of claim 10, wherein the measurements are critical dimensionmeasurement, overlay measurements, or both.
 12. The x-ray basedmetrology system of claim 9, wherein the x-ray based metrology system isconfigured as any of a transmission small angle x-ray scatterometrysystem, a grazing incidence small angle x-ray scatterometry system, awide angle x-ray scatterometry system, a x-ray reflectometry system, agrazing incidence x-ray reflectometry system, a x-ray diffractometrysystem, a grazing incidence x-ray diffractometry system, a highresolution x-ray diffractometery system, a x-ray photoelectronspectrometry system, a x-ray fluorescence metrology system, a totalreflection x-ray fluorescence metrology system, a grazing incidencex-ray fluorescence metrology system, a x-ray tomography system, a x-rayellipsometry system, and a hard x-ray photoemission spectrometry system.13. The x-ray based metrology system of claim 9, wherein the collectedamount of x-ray emission is transmitted through a portion of therotating anode assembly from the liquid metal anode material to the atleast one x-ray optical element.
 14. The x-ray based metrology system ofclaim 13, the rotating anode assembly further comprising: an outputwindow coupled to the rotating anode support structure, wherein theoutput window is transparent to the x-ray emission, and wherein thecollected amount of x-ray emission is transmitted through the outputwindow from the liquid metal anode material to the at least one x-rayoptical element.
 15. The x-ray based metrology system of claim 9, therotating anode assembly further comprising: a containment window coupledto the rotating anode support structure, wherein the containment windowconstrains the liquid metal anode material to a fixed position withrespect to the rotating anode support structure while the rotating anodesupport structure is rotated at the constant angular velocity, whereinthe containment window is transparent to the stream of electrons, andwherein the stream of electrons is transmitted through the containmentwindow from the electron beam source to the liquid metal anode material.16. The x-ray based metrology system of claim 9, wherein the rotatinganode support structure supports the liquid metal anode material suchthat the liquid metal anode material assumes a shape that depends on anangular velocity of rotation of the rotating anode support structure 17.The x-ray based metrology system of claim 9, wherein the rotating anodesupport structure supports the liquid metal anode material such that across-section of the liquid metal anode material at any location along afocal track of the liquid metal rotating anode x-ray illumination sourceassumes a constant shape independent of an angular velocity of rotationof the rotating anode support structure.
 18. A method comprising:emitting a stream of electrons toward a liquid metal anode material froma cathode of an electron beam source, the interaction of the stream ofelectrons with the liquid metal anode material causing an x-rayemission; rotating a rotating anode support structure about an axis ofrotation at a constant angular velocity, the rotating anode supportstructure supporting the liquid metal anode material in a fixed positionwith respect to the rotating anode support structure while the rotatinganode support structure is rotating at the constant angular velocity;and collecting an amount of the x-ray emission from the liquid metalanode material.
 19. The method of claim 18, further comprising:illuminating an inspection area of a specimen with an incident x-raybeam comprising the amount of the x-ray emission collected from theliquid metal anode material; detecting an amount of radiation from thespecimen in response to the incident x-ray beam; and generating signalsindicative of a first property of the specimen based on the detectedamount of radiation.
 20. The method of claim 18, wherein the collectedamount of x-ray emission is transmitted through an output window fromthe liquid metal anode material to the at least one x-ray opticalelement.
 21. The method of claim 18, further comprising: constrainingthe liquid metal anode material to a fixed position with respect to therotating anode support structure by a containment window while therotating anode support structure is rotated at the constant angularvelocity; and transmitting the stream of electrons through thecontainment window from the electron beam source to the liquid metalanode material.